The present invention relates to a high-pressure dome type compressor comprising a motor using a rare earth magnet.
Conventional compressors for a refrigerant unit include a high-pressure dome type compressor comprising a compression element and a motor for driving the compression element in a casing. The motor of this high-pressure dome type compressor is disposed in a high pressure area filled with gas discharged from the compression element in the casing. The motor is a dc (direct current) motor driven under control of an inverter. A permanent magnet of a rotor of the motor is composed of a ferrite magnet having a great intrinsic coercive force.
However, since the ferrite magnet has a relatively little magnetic force, a large permanent magnet is required in order to increase output of the motor. Therefore, the rotor is upsized and thus the motor is upsized. Consequently, a problem arises that the compressor is upsized since the motor is upsized to increase output of the compressor.
Then, a high-pressure dome type compressor which could be downsized even with high output by using a rare earth magnet having a great magnetic force as a permanent magnet for a rotor of a motor was proposed recently.
In the high-pressure dome type compressor, however, the rare earth magnet is demagnetized due to heat generated by the motor or compression heat from a refrigerant, thereby degrading performance of the motor since the rare earth magnet used for the rotor of the motor is demagnetized with a temperature rise. Also, after a certain limit is exceeded, irreversible demagnetization occurs and the magnetic force is lost and thereby functions of the motor are lost. Furthermore, the rare earth magnet is demagnetized even when an opposing magnetic field is received. Therefore, when a current flowing in the motor increases, the rare earth magnet for the rotor is demagnetized by an opposing magnetic field generated in a stator of the motor, thereby degrading performance of the motor. Thus, a problem arises that a rare earth magnet cannot be used in a large-sized high-pressure dome type compressor with high output. More specifically, a motor having a rare earth magnet cannot be used in a high-pressure dome type compressor which uses R32 as a refrigerant and has a motor with a rated output of 1.9 kW or higher.
Accordingly, an object of the present invention is to provide a small-sized high-pressure dome type compressor with high output which has stable performance without causing irreversible demagnetization in a rare earth magnet even when the rare earth magnet is used for a motor.
Another object of the present invention is to provide a small-sized high-pressure dome type compressor with high output which has stable performance without causing irreversible demagnetization in a rare earth magnet even when used in a refrigerant unit using R32, as a refrigerant, which obtains a high temperature when compressed.
In order to achieve the aforementioned objects, there is provided a high-pressure, dome-type compressor comprising a compression element and a motor for driving the compression element in a casing, xe2x80x9cdome-typexe2x80x9d being defined as having an end surface of the compressor casing which forms a dome shape. The motor is disposed in a high pressure area filled with a gas discharged from the compression element in the casing and has a rated output of 1.9 kW or higher. In addition, a rotor of the motor includes a rare earth/iron/boron permanent magnet having an intrinsic coercive force of 1.7 MA.mxe2x88x921 or greater, wherein M is mega, A is ampere, and m is meter.
In the above high-pressure dome type compressor, since the rare earth/iron/boron permanent magnet provided to the rotor of the motor has an intrinsic coercive force of 1.7 MA.mxe2x88x921 or greater, the permanent magnet is hardly demagnetized and no irreversible demagnetization occurs even in the high-pressure dome type compressor, which obtains a relatively high temperature. Furthermore, the permanent magnet is hardly demagnetized and no irreversible demagnetization occurs in the motor having a rated output of 1.9 kW or higher and a relatively strong opposing magnetic field generated in a stator of the motor as well. Therefore, the motor using the rare earth/iron/boron permanent magnet has higher output and a smaller size as well as more stable performance than a conventional motor using a ferrite permanent magnet. Thus, the high-pressure dome type compressor provided with the motor has high output and a small size and that performance of the high-pressure dome type compressor becomes stable.
In one embodiment, the high-pressure dome type compressor further comprises:
a temperature sensor for detecting a temperature of the motor; and
first control means for, upon receipt of a signal from the temperature sensor, controlling a current to be supplied to the motor such that the temperature of the motor becomes equal to a predetermined temperature or lower.
In the above high-pressure dome type compressor, the sensor detects the temperature of the motor having the rare earth/iron/boron permanent magnet and notifies the temperature to the first control means. This first control means reduces the current to be supplied to the motor and reduces the number of revolutions of the motor when the temperature of the motor is higher than the predetermined temperature. Consequently, heat generated by the motor is reduced and the temperature of the motor lowers. As a result, demagnetization of the rare earth/iron/boron permanent magnet provided to the motor is prevented.
In one embodiment, the high-pressure dome type compressor further comprises:
current detecting means for detecting a current flowing in the motor;
second control means for receiving a signal from the current detecting means and controlling a current to be supplied to the motor such that an opposing magnetic field generated in the motor becomes equal to a predetermined strength or less.
In the above high-pressure dome type compressor, the current detecting means detects a value of the current supplied to the motor having the rare earth/iron/boron permanent magnet and notifies the value to the second control means. This second control means calculates strength of an opposing magnetic field generated in the motor based on the value of the current to be supplied to the motor. When the strength of this opposing magnetic field is greater than the predetermined value, the second control means reduces the current to be supplied to the motor and weakens the strength of the opposing magnetic field in the motor. Therefore, demagnetization of the rare earth/iron/boron permanent magnet provided to the motor is prevented.
In one embodiment, a discharge pipe for discharging the discharged gas from the casing is disposed on a side of the motor opposite from the compression element.
In the above high-pressure dome type compressor, since the compression element is disposed on one side of the motor and the discharge pipe is disposed on the other side, the discharged gas compressed by the compression element passes through the motor disposed in the high pressure area filled with this discharged gas and then discharged from the discharge pipe to the outside of the casing. Therefore, the motor is cooled by the discharged gas and thereby demagnetization of the rare earth/iron/boron permanent magnet provided to the motor is prevented.
In one embodiment, a discharge pipe is communicated with the high pressure area between the compression element and the motor, while the gas discharged from the compression element passes through a path in a crank shaft and is discharged to the high pressure area on a side of the motor opposite from the compression element.
In the above high-pressure dome type compressor, after the discharged gas from the compression element passes through the path in the crank shaft and is discharged to the high pressure area on the side of the motor opposite from the compression element, the discharged gas passes through the motor and is discharged from the discharge pipe to the outside of the casing. Therefore, the motor is cooled by the discharged gas and thereby demagnetization of the rare earth/iron/boron permanent magnet provided to the motor is prevented.
In one embodiment, the permanent magnet for the rotor of the motor is coated with aluminium.
In the above high-pressure dome type compressor, since the permanent magnet for the rotor of the motor is coated with aluminium, the permanent magnet does not become rusty even in the high pressure area of the high-pressure dome type compressor having a relatively high temperature. Since the refrigerant gas does not flow into the permanent magnet, deterioration by the refrigerant is also prevented. Further, when the high-pressure dome type compressor is used for a refrigerant unit using R32 as a refrigerant, the permanent magnet is not attacked by the R32 due to the aluminium coating. Therefore, performance of the motor is maintained and performance of the high-pressure dome type compressor becomes stable.
In one embodiment, a refrigerant unit comprises the high-pressure dome type compressor of the present invention and uses R32 as a refrigerant.
In the above refrigerant unit, even though R32, which is compressed in the high-pressure dome type compressor and obtains a high temperature, is used as the refrigerant, the rare earth/iron/boron permanent magnet of the motor provided to this high-pressure dome type compressor is hardly demagnetized since this high-pressure dome type compressor is provided. Therefore, the motor has a small size and high output as well as stable performance. As a result, the high-pressure dome type compressor provided with the motor has a small size and high output as well as stable performance. Thus, performance of the refrigerant unit provided with the high-pressure dome type compressor becomes stable.